Sierra 18-5278 V-6 Delco EST Ignition Tune-Up Kit, Replaces Mercruiser 850484T3

The Sierra 18-5278 is an ignition tune-up kit engineered for V-6 engines equipped with a Delco EST ignition system. Tune-up kits like this one are used to restore reliable spark delivery during routine engine maintenance, replacing worn distributor components that can cause misfires, hard starting, or rough idle over time. The kit includes a distributor cap (18-5362) and rotor (18-5408), finished in white, giving the buyer the two core wear items needed for a complete distributor cap-and-rotor service in one package. Each Sierra product is built to meet or exceed the performance of the original equipment part it replaces, making this kit a straightforward drop-in service solution rather than a partial fix requiring separate part sourcing. Because ignition components are fit-specific, buyers should confirm part numbers against their engine before ordering to ensure proper fit. This kit is cross-referenced to multiple OEM and aftermarket part numbers, so it can be located under several different catalog listings depending on the engine manufacturer's documentation a buyer is working from.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-5278
• Engine Configuration: V-6
• Ignition System: Delco EST
• Color: White
• Included Components: Distributor Cap (18-5362), Rotor (18-5408)
• UPC: 808282105075
• Weight: 0.52 pounds
• OEM Cross Reference: GLM 71820, Mallory 9-29321, Mercruiser 850484T3, Mercruiser 850484T1

Fitment

For V-6 engines equipped with a Delco EST ignition system.

Replaces (OEM)

• GLM 71820
• Mallory 9-29321
• Mercruiser 850484T3
• Mercruiser 850484T1

Frequently Asked Questions

What engines does the Sierra 18-5278 tune-up kit fit? The 18-5278 is designed for V-6 engines running a Delco EST ignition system. Because ignition parts are fit-specific, confirm your engine's ignition system type against the part number before ordering.

What is included in the 18-5278 kit? This kit contains a distributor cap (Sierra 18-5362) and a rotor (Sierra 18-5408), giving you both core wear components needed for a distributor cap-and-rotor service in one package.

Is the Sierra 18-5278 the same as Mercruiser 850484T3? Yes, the 18-5278 cross-references to Mercruiser 850484T3 and 850484T1, as well as GLM 71820 and Mallory 9-29321, so it can be ordered as a direct equivalent under any of those part numbers.

What color is the distributor cap in this kit? The distributor cap and rotor included in the Sierra 18-5278 tune-up kit are white.

How much does the 18-5278 tune-up kit weigh? The Sierra 18-5278 ignition tune-up kit weighs 0.52 pounds.

Does the 18-5278 meet OEM specifications? Sierra states that this product meets or exceeds the performance of the original equipment part it replaces, making it a direct service replacement rather than a generic substitute.

Is Sierra 18-5278 genuine Sierra or a generic aftermarket part? The 18-5278 is a genuine Sierra-branded tune-up kit, manufactured to meet or exceed the original equipment component it replaces.

What is the difference between 18-5278 and other Sierra tune-up kits like 18-5280 or 18-5281? The 18-5278 is built specifically for V-6 Delco EST ignition systems, while 18-5280 covers In-Line 4 Delco EST engines and 18-5281 covers V-8 Delco EST engines. Matching the correct kit to your engine's cylinder configuration and ignition system is essential.

Can I use the 18-5278 kit if my engine has a Prestolite Electronic ignition instead of Delco EST? No, the 18-5278 is built for Delco EST ignition systems on V-6 engines; a V-8 Prestolite Electronic engine would require a different kit (18-5279), since ignition components are not interchangeable across ignition system types.

What OEM part numbers can I search to find the 18-5278 kit? The 18-5278 kit cross-references to GLM 71820, Mallory 9-29321, Mercruiser 850484T3, and Mercruiser 850484T1.